This application claims benefit of Japanese Application No. 2000-58385 filed in Japan on Mar. 3, 2000, the contents of which are incorporated by this reference.
1. Field of the Invention
The present invention relates to a viewing optical system and an image display apparatus using the same. More particularly, the present invention relates to a viewing optical system devised to allow observation of a bright image of a display device of the type in which an image is displayed by reflected light, e.g. a reflection type liquid crystal display device, through an ocular optical system arranged to be compact in size and to minimize the loss of light quantity. The present invention also relates to an image display apparatus, e.g. a head-up display, using the viewing optical system.
2. Discussion of Related Art
In recent years, with the development of head-up displays and glasses-type displays, compact ocular optical systems have been actively developed. As a result, ocular optical systems using a thin and compact decentered prism have been proposed as disclosed, for example, in Japanese Patent Application Unexamined Publication Numbers (hereinafter referred to as xe2x80x9cJP(A)xe2x80x9d) Hei 7-333551, 8-50256 and 8-234137. These are compact ocular optical systems in which reflecting surfaces have a power and the optical path is folded, and in which rotationally asymmetric decentration aberrations produced by decentered reflecting surfaces with a power are corrected by using an anamorphic reflecting surface or a rotationally asymmetric reflecting surface having one plane of symmetry.
Regarding liquid crystal display devices for displaying an image for observation, reflection type liquid crystal display devices have been developed to form images that are brighter and easier to observe. As a reflection type liquid crystal display device including an illumination structure therefor, JP(A) Hei 10-268306 has been laid open to public.
Under these circumstances, the present applicant proposed in Japanese Patent Application Nos. Hei 11-96291, 11-176390 and 11-281031 an image display apparatus including a reflection type liquid crystal display device and an ocular optical system formed from a decentered prism, wherein an illuminating light guide prism is placed between the reflection type liquid crystal display device and the decentered prism.
Incidentally, the present applicant proposed in JP(A) Hei 11-194295 an image display apparatus for displaying color images, wherein a chromatic aberration producing device, e.g. a spectral prism, is provided to display a chromatic aberration-free color image of a color image display device by using a light source device formed from a plurality of juxtaposed illuminating light sources, e.g. LEDs, of different colors, e.g. R (red), G (green) and B (blue).
The present invention was made in view of the above-described circumstances. Accordingly, an object of the present invention is to provide a viewing optical system including a reflection type liquid crystal display device, a decentered prism and an illuminating light guide prism placed therebetween. More specifically, the present invention provides a compact, bright and high-performance viewing optical system capable of color display by using a light source device formed from a plurality of juxtaposed light sources of different colors as an illuminating light source, and also provides an image display apparatus using the viewing optical system.
To attain the above-described object, the present invention provides a viewing optical system including a reflection type image display device placed in an image plane and an ocular optical system for leading an image displayed on the reflection type image display device to the position of an exit pupil where an observer""s eyeball is to be placed. An illuminating device is placed at the position of an entrance pupil conjugate to the exit pupil with respect to the ocular optical system. The illuminating device is formed from a plurality of juxtaposed illuminating light sources of different colors. The viewing optical system further includes an illuminating light guide optical device for guiding an illuminating light beam from the illuminating device. The illuminating light guide optical device is placed between the entrance pupil and the reflection type image display device so that the illuminating light beam can be applied to the display surface of the reflection type image display device from the front side thereof. The ocular optical system includes a decentered prism formed from a medium surrounded by three optical surfaces and having a refractive index larger than 1. The decentered prism has an entrance surface through which a display light beam reflected from the reflection type image display device enters the decentered prism after passing through the illuminating light guide optical device, and a first reflecting surface for reflecting the light beam entering through the entrance surface. The decentered prism further has a second reflecting surface for reflecting the light beam reflected from the first reflecting surface, and an exit surface through which the light beam reflected from the second reflecting surface exits the decentered prism. The first reflecting surface and the exit surface are formed from a single surface serving as both a refracting surface and a reflecting surface. A chromatic aberration producing device is placed between the entrance pupil and the illuminating light guide optical device. The chromatic aberration producing device is arranged to superimpose the images of the plurality of illuminating light sources on one another in the exit pupil.
Thus, the present invention provides a compact, bright and high-performance viewing optical system for head-up displays and glasses-type displays and also provides an image display apparatus using the viewing optical system by combining together a reflection type image display device, an illuminating light guide optical device, a decentered prism as an ocular optical system, and a chromatic aberration producing device. Even in a case where a light source device formed from a plurality of juxtaposed light sources of different colors is used as an illuminating light source, the viewing optical system allows observation of a clear color image free from chromatic aberration even if the observer""s pupil position deviates from the exit pupil position.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.